The invention relates to a gas generator, in particular for a vehicle occupant restraint system.
Known gas generators comprise a combustion chamber filled with a solid propellant, a supply chamber filled with a fluid and a mixing chamber in which the hot gas generated when the solid propellant bums is mixed with the fluid, a combustion chamber wall being provided that has a plurality of outflow openings through which the hot gas escapes. Such gas generators have the advantage that the hot gas is mixed with cold fluid in the mixing chamber and the temperatures of the outflowing mixture are relatively low. Moreover, through the admixture of the fluid, a higher volume of outflowing gas can also be produced, which improves the performance of the gas generator. Up until now, the mixing in the mixing chamber is done in that the wall of the mixing chamber has various openings for the fuel and for the fluid, the openings being oriented with respect to each other in such a way that the streams of fuel and fluid meet in the mixing chamber.
The invention provides a gas generator with which the mixing is improved. This is achieved with a gas generator comprising a combustion chamber filled with a solid propellant, a supply chamber filled with a fluid and a mixing chamber in which a hot gas generated upon combustion of the solid propellant is mixed with the fluid. A combustion chamber wall is provided that has a plurality of outflow openings through which the hot gas escapes. A fluid feed chamber is provided so as to lie, in terms of flow, between the combustion chamber and the mixing chamber, the hot gas passing through the fluid feed chamber. The fluid from the supply chamber flows into the fluid feed chamber and the fluid feed chamber is radially open towards the outflow openings across the entire circumference of each of the outflow openings, so as to direct an annular fluid stream onto the hot gas. The fluid feed chamber provides a fluid feed to the hot gas directly downstream of the outflow openings in that the gas stream entrains fluid along its entire outer circumference, so that a mixture of gas and fluid is formed across a large surface.
The fluid feed chamber is delimited, on the side of the combustion chamber having the outflow openings, by the combustion chamber wall and, on the side of the mixing chamber, by a dividing wall to the mixing chamber; i.e. it is disposed immediately between the mixing chamber and the combustion chamber, so that the space requirement for the additional chamber is small and so that it is ensured that the fluid is, in fact, admixed with the hot gas directly downstream of the outflow openings.
Preferably, a flow connection is provided between the fluid feed chamber and the mixing chamber via overflow openings. The overflow openings are oriented concentrically to associated outlet openings, i.e. for each outflow opening, there is provided an overflow opening in the flow direction of the hot gas, so that the stream of hot gas is not deflected but rather can enter the mixing chamber without additional resistance.
If, according to one embodiment, the overflow openings each have a larger cross sectionxe2x80x94preferably a larger diameter in the case of circular openingsxe2x80x94than the associated outflow openings, then this facilitates the admixture of fluid that is entrained by the stream of hot gas. Since a larger volume flow arises as a result of the admixed fluid, the larger overflow openings also provide a larger flow cross section for the volume flow.
The combustion chamber wall and the dividing wall can have a dome-like shape and be situated in a tubular outer housing of the gas generator, a small gap being provided between the combustion chamber wall and the dividing wall. The dome-like shape has the advantage that the outflow or overflow openings can be made at a right angle to the surface of the dome, and these openings are directed towards the outside to the outer housing in order to obtain a flow path that is enlarged with respect to an axial alignment and along which the gas and the fluid can be mixed.
A centric tube that opens into the fluid feed chamber connects the latter with the supply chamber so that, via the tube, the fluid can enter the fluid feed chamber.